Flow cytometry reagent and system

ABSTRACT

An improved reagent system for preparation of cells for flow cytometry having a physiologically compatible salt solution composition including a lysing agent, an agent for minimizing white blood cell lysis, and optionally a preservative.

FIELD OF THE INVENTION

[0001] The present invention generally relates to compositions usefulfor selectively lysing one or more components of blood while alsoachieving the stabilization of other components and, more particularly,for lysing erythrocytes while affording the stabilization necessary topreserve antigenic sites on the surface of leukocytes.

BACKGROUND OF THE INVENTION

[0002] The ability to differentiate and phenotype blood cells is usefulfor evaluating disease states and other health conditions in livingbeings. One popular technique for cell differentiation and lymphocyteimmunophenotyping is flow cytometry. With flow cytometry, cells from anappropriately prepared blood sample, are passed one at a time through aflow cell, which is adapted for sensing or detecting impedance changes,light scatter or some other characteristic of the cell. Some flowcytometry instruments are equipped with detectors for measuringemissions from fluorescent tags that may be associated with the cells,while other detectors measure scatter intensity or pulse duration. Dataabout cells that pass through the flow cell can be plotted on a cytogramaccording to the measured property.

[0003] During the flow cytometry process, it is important thatinterference from the presence of erythrocytes (red blood cells) in theblood sample be avoided. Accordingly, during sample preparation, whichmay be done by manual, semi-automated or automated techniques), it ispopular to employ a lytic reagent for lysing red blood cells and therebyisolating the leukocyte (white blood cell) populations. Leukocytes areknown to include a myeloid fraction of monocytes and granulocytes(neutrophils, basophils and eosinophils) and a lymphoid fraction (namelyNK, B and T cell lymphocytes). Each of the lymphocyte populations can bedistinguished based upon the distinctive cell surface antigens ormarkers. Moreover, within each category of lymphocytes, there aresub-categories, such as “helper” T cells or “suppressor” T cells, thelatter of which also includes several subsets, distinguishable by theirrespective surface markers. With flow cytometry of properly preparedcells, using polyclonal or monoclonal antibodies, it is possible toassay lymphocytes to analyze cells in the various subcategories.

[0004] For instance, to prepare a sample for fluorescent flow cytometry,according to one conventional practice, a volume of fresh sample bloodis provided, and a suitable amount of a desired fluorochrome labeledantibody is added. The sample and antibody mixture is incubated to allowantibody/antigen bindings to take place. After incubation, a lyticreagent (some of which are regarded as potentially toxic, i.e., thosecontaining formaldehyde) is added to lyse erythrocytes in the sample.The debris from the lysing of the erythrocytes is optionally removed, bywashing, leaving a sample of leukocytes with antibodies bound to cellswith complementary surface antigens. The sample is fixed and run througha fluorescent detecting flow cytometry instrument.

[0005] Among the items of potential interest to the present inventionare Brown et al, “Flow Cytometry: Principles and Clinical Applicationsin Hematology”, Clinical Chemistry 46:8(B), 1221-1229 (2000); U.S. Pat.Nos. 4,654,312; 4,902,613; 5,030,554; 5,188,935; 5,196,182; 5,250,438;5,260,048; 5,459,073; 5,460,797; 5,731,206; 5,776,709; 5,811,099;5,849,517, 5,939,326; 6,110,730; and commonly owned, co-pending U.S.patent application Ser. No. 09/500,248 (“Fixative System, Method andComposition for Biological Testing”), the teachings of each of which arehereby expressly incorporated by reference for all purposes.

[0006] Accordingly, in view of the above, there is a need in the art foran improved lytic reagent that lyses red blood cells systematically andreproducibly preserves the surface antigen characteristics ofleukocytes; that enables fixing of the leukocytes during the erythrocytelysing step; that is nontoxic; and that can be used to prepare samplesfor analysis beyond one day.

SUMMARY OF THE INVENTION

[0007] As will be appreciated by one skilled in the art, the above needsare met individually or in combination, and other advantages arepossible, by the employment of one or more novel compositions, each ofwhich include effective amounts of a lytic agent, an agent forminimizing lysing of white blood cells (e.g., lipoprotein) andoptionally a preservative. The composition of the present invention isparticularly suited for use as a lytic reagent system for flowcytometry, but may also find suitable application in other analyticalsystems, such as hematology analyzers and microscopy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIGS. 1-4 are cytograms for illustrating the advantages of thecompositons of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0009] Parts and percentages herein are expressed by weight, unlessotherwise noted. The term “lysis” (and its conjugates) as used hereinshall mean to render cells no longer detectable by physical techniques.In the context of erythrocyte lysis, “lysis” shall refer to therendering of erythrocyte residue (as represented, for instance, byreference numeral 10 in the Figures) so that any signals they mightgenerate are minimized to avoid detectably interfering with thoseproduced by the leukocytes.

[0010] A preferred composition in accordance with the present inventionincludes:

[0011] a) a lytic agent for lysing red blood cells;

[0012] b) an agent for minimizing lysing of white blood cells; and

[0013] c) optionally a preservative for preserving white blood cells.

[0014] The active ingredients preferably are dissolved or suspended in asuitable physiological salt medium, such as a suitable saline, water oralcohol solution. A particularly preferred medium includes a metal salt(e.g., about 0.1 to about 2, more preferably about 0.5 to about 1.5, andstill more preferably, about 0.9 percent by weight of the overallcomposition of metal halide salt) in distilled water.

[0015] The lytic agent of the present invention may be any suitablelytic agent. Preferably, however, the lytic agent is saponin, and it ispresent in an amount of about 0.1 to about 2 percent by weight of theoverall composition, more preferably about 0.3 to about 1.5 percent, andstill more preferably about 0.5 to about 1 percent. Examples of othersuitable lytic agents include ammonium halides, such as dodecyltrimethylammonium chloride.

[0016] Though other constituents are possible, the agent for minimizinglysing of white blood cells preferably includes a lipoprotein. Thelipoproteins suitable for use in the present invention can be eitherhigh or low density lipoproteins, both of which are available from anumber of commercial sources. Lipoproteins from humans or the serum ofvarious animals, (e.g. horse and bovine) and egg yolk lipoprotein may beused. It is also possible to use compositions containing lipoproteins asthe lipoprotein source. Examples of such lipoprotein sources are animal(include man) blood serums and plasmas. Where suchlipoprotein-containing compositions are employed, the amount ofcomposition employed in the reference controls of the invention willdepend upon the concentration of the lipoprotein. Preferred blood plasmaor serum concentrates are those concentrated two to three fold so as tocontain about 14 to 17% by weight of protein.

[0017] In a particularly preferred embodiment, the lipoprotein is a highdensity lipoprotein, such as that commercial available under thetradename SUPERTRATE® or MODUCYTE® from Bayer, or the like. In generalsuch lipoprotein source compositions include a high density lipoproteindispersed in a medium including about 25 mg/dl lipoproteincholesterol/100 ml of product. Accordingly, about 0.01 to about 5percent by weight of the overall composition is lipoprotein; morepreferably about 0.1 to about 1 percent by weight; and still morepreferably about 0.2 to about 0.5 percent by weight.

[0018] The composition of the present invention includes, in onepreferred embodiment, a preservative (also regarded as a fixative)dispersed in a liquid medium. More preferably, the preservative is achemical agent known widely in the art as a non-coagulating preservativeor fixative. Thus, the preferred preservative when contacted with abiological specimen generally will exhibit only insubstantialdenaturation (if any) of plasma protein substances in the biologicalmaterial. It should be realized that in some instances a coagulatingpreservative may be employed in combination with or a non-coagulatingpreservative in accordance with certain aspects of the presentinvention, provided the resulting properties of the overall compositionare not materially affected for purposes of handling or laterpathological testing. In some instances, a coagulating preservativeabsent appreciable amounts of non-coagulating preservative may beemployed advantageously.

[0019] Though other preservatives may be employed (e.g., aldehydes suchas paraformaldehyde), the preservative of the compositions of thepresent invention preferably includes at least one non-crosslinkingagent. One preferred class of preservatives includes a heterocyclicsubstituted urea in a buffered physiological salt solution. In anotherembodiment, the preservative is selected from the group consisting ofdiazolidinyl urea (DU), imidazolidinyl urea (IDU), polymethoxy bicyclicoxazolidine (e.g., NUOSEPT® 145 from Creanova Inc.) and mixturesthereof. Most preferably, the preservative is DU. The amount ofpreservative employed ranges up to about 5 percent by weight of theoverall composition, more preferably about 0.5 to about 4 percent, andstill more preferably about 2 to about 3 percent.

[0020] One popular technique for flow cytometry analysis, which may beemployed in accordance with one aspect of the present invention involvesthe use of fluorescence techniques for cell analysis, in which cells areanalyzed for the response of cell nucleic acid content, surface antigensor both to fluorescently tagged monoclonal or polyclonal antibodies ormarkers. The primary and secondary antibodies may be polyclonal, but arepreferably monoclonal antibodies. Without limitation, illustrativeexamples of primary antibodies include, but are not limited to, a firstfluorochrome label conjugated with the primary antibody.

[0021] If employed, one or more secondary antibody (polyclonal ormonoclonal) may also be employed.

[0022] In general this labeling step involves staining a cell with anappropriate dye, or attaching a detectable fluorochrome label to thecell's surface, e.g., a fluorescently tagged antibody, the presence ofwhich when detected would indicate the occurrence of a specificantigen-antibody reaction. Without limitation, examples of popularfluorochromes include fluorescein isothiocyanate, phycoerythrin (e.g.,B- or R-type), propidium iodide, Texas Red, allophycocyanin or peridininchlorophyl protein. Any of these fluorochromes, as well as others knownin the art (including fluorochomes for two color, three color or fourcolor approaches), can be used to label the primary and secondaryantibodies of the invention using conjugation methods well known in theart.

[0023] The resulting pH of the composition (in its liquid state) of thepresent invention ranges from about −6 to about 9.5 and more preferablyabout 7 to about 8.5, and still more preferably about 8. The resultingcomposition may be contacted with cell samples and the samples preservedfor as much as two, four or seven days or longer prior to analysis ofthe samples by flow cytometry. The resulting composition is also capableof stabilities for periods of 6 months or longer.

[0024] In a highly preferred embodiment, the resulting composition is:Range Diazolidinyl urea 1.0-6.0 gm/dl Saponin 10.0-300.0 mg/dlLipoprotein 5.0-100.0 mg/dl of cholesterol

[0025] Compositions in accordance with the present invention may alsoinclude other ingredients as desired and depending upon the intendedapplication, such as (without limitation) mordants, buffers,surfactants, penetration increasers, osmotically active substances,nuclear detail improvers, and nuclear size increasers, such as addressedin U.S. Pat. No. 5,196,182, hereby expressly incorporated by reference.Examples of suitable mordants are salt of a metal having an oxidationstate of two or more, e.g., zinc, strontium, calcium, barium, andchromium salts. The preferred salt is zinc sulfate. Suitable buffersinclude alkali metal phosphate salts, such as sodium phosphate andpotassium phosphate. Osmotically active substances that may be includedin the formulation of the invention are alkali metal salts, such assodium chloride. In addition, sugars, such as the polysaccharides,sucrose, glucose, and the like, may be employed. Nuclear detailimprovers and nuclear size increasers include acetic acid and lithiumsalts such as lithium chloride. Zinc salts, such as zinc sulfate, notonly improve nuclear definition, but also improve staining. Illustrativeof substances which increase the rate of penetration of the fixing agentare dimethylsulfoxide and ethanol.

[0026] The compositions of the present invention may be supplied as partof a kit, whose other components might include blood controls, otherchemical reagents for a cytometry lab, a hematology instrument, a flowcytometer, sample preparation instruments, data management units or thelike. It is also contemplated that any such instrument might be offeredfor sale as part of an agreement calling for a periodic replenishment ofsupply of the compositions of the present invention. The compositionsmay also be offered for sale in combination with one or more additionalitems such as those selected from glass slides, petri dishes, vials,flasks, beakers, storage and transport containers, handling instruments,protective clothing, preparatory chemicals, reagents, controls, readoutdevices, barcode scanners, data management kits, data forms, software,loaders, loader racks, labelers, coverslips or mixtures thereof. Inanother preferred embodiment, a composition of the present invention isprovided in a kit including an immunostain, dye, a fluorochrome (orother tag), or the like, either with or without an associated monoclonalantibody. Kits or their respective components, including the compositionof the present invention, may be offered for sale through a salesdistributor, directly by the manufacturer, through a retail outlet,through a wholesale outlet, by mail order, over the internet, orotherwise. The compositions are preferably provided in a 5× concentrate,(though other concentrates may be used) in suitable bottles (e.g., 200ml bottles) that can be packaged individually or in groups of two,three, four or more bottles.

[0027] The compositions of the present invention are useful forperforming hematology analysis of samples in manual and automatedinstruments, with flow cytometers with hematology blood analyzers, withmicroscopy using optical microscopy, electron microscopy or the like.Samples prepared for analysis with the compositions of the presentinvention may be prepared using manual, semiautomated or automatedtechniques.

[0028] In one aspect of the present invention, a composition of thepresent invention is used for research, such as cancer research, AIDSresearch or otherwise. In another embodiment it is used for clinicaldiagnosis of patients. The composition may be used for analyzing bloodof humans, other mammals, birds, reptiles, or other animals, in either ahospital, veterinary or other clinical or institutional setting.

[0029] In one embodiment, a composition in accordance with the presentinvention is contacted with a sample of blood infected by HIV. When thesample is processed, the DU or formaldehyde present in the samplestabilizes the white cells and inactivates HIV.

[0030] The compositions of the present invention may be used alone or incombination with other commercially available lytic reagents, includingfor example, IMMUNOPREP™ (Beckman Coulter), LYSE and FIX (BeckmanCoulter), Q-Prep (Beckman Coulter) OPTILYSE (Beckman Coulter), FACS Lyse(Becton Dickinson), ERYTHROLYSE (Serotec), FLOWLYSE (Mallinckrodt),WHOLE BLOOD LYSE KIT (Caltag), UTI-LYSE (Dako), Q-LYSE (BioErgonomics,Inc.), ammonium chloride or the like. Moreover, active ingredients ofthe above may be substituted for or used in combination with theingredients of the present compositions.

[0031] To prepare a sample for fluorescent flow cytometry, according toone method of the present invention, a predetermined volume of freshsample blood is provided, and a suitable amount of the desiredfluorochrome labeled monoclonal antibody is added. The sample andantibody mixture is then incubated for a predetermined time (e.g., about10 to about 30 minutes) at a predetermined temperature to allow antibodyand antigen bindings to take place. Sample may then be washed andresuspended as desired. After incubation, the composition of the presentinvention is contacted with the sample to lyse erythrocytes in thesample. Such contacting step occurs for a period of time sufficient sothat any erythrocytes that remain in the sample will not materiallydistort measurements, but not so long that leukocytes will be damaged.The debris from the lysing of the erythrocytes is optionally removed, bywashing, leaving a sample of leukocytes with antibodies bound to cellswith complementary surface antigens. The sample is then run through afluorescence detecting flow cytometry instrument. In another embdiment,the composition of the present invention is contacted with the cellsprior to labeling and incubation.

[0032] In accordance with the above, it will be appreciated that amongthe advantages of the compositions of the present invention are that thecompositions of the present invention can be formulated as nontoxiccompositions. Reproducible cytometric results are obtainable afterdelays from sample collection or preparation to testing. Thecompositions can be used in wash and no wash systems. Samples can belysed before or after staining with markers, or otherwise tagging, withno adverse effect upon fluorescence or dispruption of cell surfacemarkers. The compositions can be used as a fixation-permeation agent. Aswell as providing good fluorescence cytometric analysis, thecompositions exhibit good retention of light scatter characteristics,good signal to noise ratio, and the ability to gate (or otherwiseisolate a sample portion by electronic logic with a physicalmeasurement) well for purposes of forward light scatter and side lightscatter instruments. The compositions are thus suitable for use in avariety of commercially available instruments, such as (withoutlimitation) available from Becton Dickinson under its FACS™ designation,such as (without limitation) FACSCalibur, FACSVantage, or instrumentsemploying like technology; from Beckman Coulter under the designationEPICS® (as well as associated sample preparation stations such as itsQ-PREP line; from Abbott Laboratories under the CELL-DYN™ designation(e.g., Cell-Dyn 4000).

[0033] The present invention is further illustrated by reference to thefollowing Examples, which are illustrative only and not intended aslimiting.

EXAMPLES Example 1

[0034] Human blood samples are prepared for flow cytometry. A firstsample (Sample A) is treated with the composition prepared by adding tounheated distilled water in the following order: 9 g/l NaCl; 30 g/l DU;0.25 g/l high density lipoprotein cholesterol; and 0.7 g/l saponin. Asecond sample (Sample B) is treated with a prior art compositionincluding conventional amounts of diethylene glycol, formaldehyde anddistilled water. The samples are analyzed by a flow cytometer on the daythey are drawn. Sample A yields a cytogram such as depicted in FIG. 1,having four identifiable clusters corresponding respectively to cellpopulations of debris from lysed red blood cells 10, lymphocytes 12,monocytes 14 and granulocytes 16. Sample B yields a cytogram such asdepicted in FIG. 2, where like components are represented by likereference numerals. The cytogram of FIG. 1 exhibits better resolution,brighter intensity and improved light scatter.

Example 2

[0035] The samples of Example 1 are analyzed by a flow cytometer 48hours after they are drawn. Sample A yields a cytogram such as depictedin FIG. 3 and Sample B yields a cytogram such as depicted in FIG. 4(again, where like components are represented by like referencenumerals). A comparison of FIGS. 1 and 3 shows similar results areobtained and confirm sample stability. A comparison of FIGS. 2 and 4shows a significant visible deviation.

Example 3

[0036] Sample A is employed in a wash preparatory method and a no washpreparatory method, and similar results are obtained as in Example 1,the same day as the sample is drawn, as well as 48 hours.

[0037] The illustrative embodiments set forth in the above constituteexamples of the principles of the present invention. Numerousalternatives will readily occur to the person skilled in the art,without departing from the scope of the present invention as set forthin the following claims.

What is claimed is:
 1. A reagent composition for preparing leukocytesfor cytometric analysis, comprising: a. a lipoprotein; and b. an agentfor lysing erythrocytes for permitting cytometric analysis of saidleukocytes.
 2. A reagent composition for preparing leukocytes foranalysis by flow cytometry, comprising: a. about 5 to about 100 mg/dl oflipoprotein cholesterol; b. about 10 to about 300 mg mg/dl of saponin;and c. about 1 to about 6 gm/dl of a preservative.
 3. An aqueous reagentcomposition for preparing leukocytes for analysis by flow cytometry,comprising: a. about 0.01 to about 5 parts by weight high densitylipoprotein; b. about 0.1 to about 2 parts by weight of saponin; c. upto about 5 parts by weight of diazolidinyl urea; and d. about 0.1 toabout 2 parts by weight of a halide salt.
 4. A method for preparing ablood sample for fluorescent analysis with a flow cytometer, comprisingthe steps of: a. contacting at least one leukocyte in said blood samplewith an aqueous reagent that includes: i. a lipoprotein agent forresisting lysing of white blood cells; and ii. an effective amount of anagent for lysing erythrocytes; and iii. a physiologically compatiblesalt; b. labeling said at least one leukocyte with a fluorescent labelassociated with a known antibody; c. analyzing said at least oneleukocyte with an analytical instrument.
 5. A system for flow cytometry,comprising: a. a flow cytometer instrument; b. a reagent for preparingleukocytes for analysis by flow cytometry, said reagent including: i. aneffective amount of a lipoprotein; and ii. an effective amount of alytic agent.
 6. The composition of claim 1 further comprising apreservative.
 7. The composition of claim 1 wherein said preservative isa noncoagulative preservative.
 8. The composition of claim 1 whereinsaid preservative is selected from the group consisting of diazolidinylurea (DU), imidazolidinyl urea (IDU), an oxazolidine and mixturesthereof.
 9. The composition of claim 1 further comprising an effectiveamount of a physiologically compatible salt.
 10. The composition ofclaim 1 wherein said lipoprotein is a high density lipoprotein.
 11. Thecomposition of claim 1 wherein said agent for lysing is saponin.
 12. Thecomposition of claim 2 further comprising a salt solution.
 13. Thecomposition of claim 2 wherein said preservative is selected from thegroup consisting of diazolidinyl urea (DU), imidazolidinyl urea (IDU),an oxazolidine and mixtures thereof.
 14. The composition of claim 13wherein said preservative is diazolidinyl urea.
 15. The composition ofclaim 2 wherein said salt solution includes sodium chloride.
 16. Thecomposition of claim 12 wherein said salt solution is aqueous.
 17. Thecomposition of claim 3, wherein said high density lipoprotein is presentin an amount of about 0.1 to about 1 parts by weight.
 18. Thecomposition of claim 3, wherein said high density lipoprotein is presentin an amount of about 0.2 to about 0.5 parts by weight.
 19. Thecomposition of claim 3, wherein said saponin is present in an amount ofabout 0.3 to about 1.5 parts by weight.
 20. The composition of claim 3,wherein said saponin is present in an amount of about 0.5 to about 1part by weight.
 21. The composition of claim 3, wherein saiddiazolidinyl urea is present in an amount of about 0.5 to about 4 partsby weight.
 22. The composition of claim 3, wherein said diazolidinylurea is present in an amount of about 2 to about 3 parts by weight. 23.The composition of claim 3, wherein said halide salt is sodium chloride.24. The composition of claim 23, wherein said sodium chloride is presentin an amount of about 0.1 to about 2 parts by weight.
 25. Thecomposition of claim 23, wherein said sodium chloride is present in anamount of about 0.5 to about 1.5 parts by weight.
 26. The method ofclaim 4 wherein said reagent further includes an effective amount of apreservative.
 27. The method of claim 4 wherein said lipoprotein of saidreagent is a high density lipoprotein.
 28. The method of claim 4 whereinsaid labeling step (b) occurs prior to said contacting step (a).
 29. Themethod of claim 4 wherein said labeling step (b) occurs after saidcontacting step (a).
 30. The method of claim 4 wherein said contactingstep (a) occurs at least 24 hours prior to said analyzing step (c). 31.The method of claim 4 wherein said contacting step (a) occurs at least48 hours prior to said analyzing step (c).
 32. The method of claim 4wherein said contacting step (a) occurs at least two weeks prior to saidanalyzing step (c).
 33. The method of claim 4 wherein said instrument isa flow cytometer.
 34. The method of claim 4 wherein said instrument is amicroscope.
 35. The system of claim 5 further comprising a samplepreparation instrument.
 36. The system of claim 5 further comprising anantibody for binding with a surface antogen of at least one of saidleukocytes.
 37. The system of claim 36 further comprising a fluorochromeassociated with said antibody.
 38. The system of claim 36 wherein saidantibody is a monoclonal antibody.